An application layer is an
abstraction layer
In computing, an abstraction layer or abstraction level is a way of hiding the working details of a subsystem. Examples of software models that use layers of abstraction include the OSI model for network protocols, OpenGL, and other graphics libra ...
that specifies the shared
communications protocols and
interface methods used by
hosts in a communications network. An ''application layer'' abstraction is specified in both the
Internet Protocol Suite (TCP/IP) and the
OSI model. Although both models use the same term for their respective highest-level layer, the detailed definitions and purposes are different.
Internet protocol suite
In the Internet protocol suite, the application layer contains the communications protocols and interface methods used in process-to-process communications across an
Internet Protocol (IP) computer network. The application layer only standardizes communication and depends upon the underlying
transport layer protocols to establish host-to-host data transfer channels and manage the data exchange in a
client–server or
peer-to-peer networking model. Though the TCP/IP application layer does not describe specific rules or data formats that applications must consider when communicating, the original specification (in ) does rely on and recommend the
robustness principle
In computing, the robustness principle is a design guideline for software that states: "be conservative in what you do, be liberal in what you accept from others". It is often reworded as: "be conservative in what you send, be liberal in what you a ...
for application design.
OSI model
In the
OSI model, the definition of the application layer is narrower in scope. The OSI model defines the application layer as only the interface responsible for communicating with host-based and user-facing applications.
OSI then explicitly distinguishes the functionality of two additional layers, the
session layer and
presentation layer, as separate levels below the application layer and above the transport layer. OSI specifies a strict modular separation of functionality at these layers and provides
protocol implementations for each. In contrast, the Internet Protocol Suite compiles these functions into a single layer.
Sublayers
Originally the OSI model consisted of two kinds of application layer services with their related protocols. These two sublayers are the common application service element (CASE) and specific application service element (SASE).
Generally, an application layer protocol is realized by the use of the functionality of a number of application service elements. Some application service elements invoke different procedures based on the version of the session service available.
CASE
The common application service element sublayer provides services for the application layer and request services from the session layer.
It provides support for common application services, such as:
* ACSE (
Association Control Service Element Association Control Service Element (ACSE) is the OSI method for establishing a call between one application programs. ACSE checks the identities and contexts of the application entities, and could apply an authentication security check.
Reference ...
)
* ROSE (Remote Operation Service Element)
* CCR (Commitment Concurrency and Recovery)
* RTSE (Reliable Transfer Service Element)
SASE
The specific application service element sublayer provides application-specific services (protocols), such as:
*
FTAM
FTAM, ISO standard 8571, is the OSI application layer
An application layer is an abstraction layer that specifies the shared communications protocols and Interface (computing), interface methods used by Host (network), hosts in a communi ...
(File Transfer, Access and Manager)
*
VT (Virtual Terminal)
* MOTIS (Message Oriented Text Interchange Standard)
* CMIP (Common Management Information Protocol)
* JTM (Job Transfer and Manipulation)
a former OSI standard
/ref>
* MMS MMS may refer to:
Science and technology Network communication protocols
* Multimedia Messaging Service for mobile phones
* Microsoft Media Server, a content-streaming protocol (mms://)
* Manufacturing Message Specification for real time proces ...
(Manufacturing Messaging Specification)
* RDA (Remote Database Access)
* DTP (Distributed Transaction Processing)
Protocols
The IETF definition document for the application layer in the Internet Protocol Suite is RFC 1123. It provided an initial set of protocols that covered the major aspects of the functionality of the early Internet:
Examples
Additional notable application-layer protocols include the following:
* 9P, Plan 9 from Bell Labs distributed file system protocol
*AFP, Apple Filing Protocol
*APPC, Advanced Program-to-Program Communication
*AMQP, Advanced Message Queuing Protocol
The Advanced Message Queuing Protocol (AMQP) is an open standard application layer protocol for message-oriented middleware. The defining features of AMQP are message orientation, queuing, routing (including point-to-point and publish-and-subsc ...
*Atom Publishing Protocol
The name Atom applies to a pair of related Web standards. The Atom Syndication Format is an XML language used for web feeds, while the Atom Publishing Protocol (AtomPub or APP) is a simple HTTP-based protocol for creating and updating web r ...
* BEEP, Block Extensible Exchange Protocol
*Bitcoin
Bitcoin ( abbreviation: BTC; sign: ₿) is a decentralized digital currency that can be transferred on the peer-to-peer bitcoin network. Bitcoin transactions are verified by network nodes through cryptography and recorded in a public distr ...
* BitTorrent
*CFDP, Coherent File Distribution Protocol
*CoAP, Constrained Application Protocol
*DDS, Data Distribution Service
* DeviceNet
* eDonkey
*ENRP, Endpoint Handlespace Redundancy Protocol
* FastTrack (KaZaa, Grokster, iMesh)
* Finger, User Information Protocol
* Freenet
*FTAM
FTAM, ISO standard 8571, is the OSI application layer
An application layer is an abstraction layer that specifies the shared communications protocols and Interface (computing), interface methods used by Host (network), hosts in a communi ...
, File Transfer Access and Management
*FTP, File Transfer Protocol
*Gemini, Gemini protocol
*Gopher, Gopher protocol
*HL7, Health Level Seven
*HTTP, Hypertext Transfer Protocol
*Hypercore, formerly dat://
*H.323
H.323 is a recommendation from the ITU Telecommunication Standardization Sector (ITU-T) that defines the protocols to provide audio-visual communication sessions on any packet network. The H.323 standard addresses call signaling and control, m ...
, Packet-Based Multimedia Communications System
* IMAP, Internet Message Access Protocol
*IRC, Internet Relay Chat
*IPFS, InterPlanetary File System
* Kademlia
*LDAP, Lightweight Directory Access Protocol
*LPD, Line Printer Daemon
The Line Printer Daemon protocol/Line Printer Remote protocol (or LPD, LPR) is a network printing protocol for submitting print jobs to a remote printer. The original implementation of LPD was in the Berkeley printing system in the BSD UNIX opera ...
Protocol
*MIME (S-MIME), Multipurpose Internet Mail Extensions and Secure MIME
* Modbus
* MQTT Protocol
* Netconf
*NFS, Network File System
*NIS, Network Information Service
*NNTP, Network News Transfer Protocol
The Network News Transfer Protocol (NNTP) is an application protocol used for transporting Usenet news articles (''netnews'') between news servers, and for reading/posting articles by the end user client applications. Brian Kantor of the Univers ...
*NTCIP, National Transportation Communications for Intelligent Transportation System Protocol
*NTP, Network Time Protocol
The Network Time Protocol (NTP) is a networking protocol for clock synchronization between computer systems over packet-switched, variable- latency data networks. In operation since before 1985, NTP is one of the oldest Internet protocols in c ...
* OSCAR, AOL Instant Messenger Protocol
AIM (AOL Instant Messenger) was an instant messaging and presence computer program created by AOL, which used the proprietary OSCAR instant messaging protocol and the TOC protocol to allow registered users to communicate in real time.
AIM ...
*POP, Post Office Protocol
*PNRP, Peer Name Resolution Protocol
Peer Name Resolution Protocol (PNRP) is a peer-to-peer protocol designed by Microsoft. PNRP enables dynamic name publication and resolution, and requires IPv6.
PNRP was first mentioned during a presentation at a P2P conference in November 2001. It ...
*RDP, Remote Desktop Protocol
Remote Desktop Protocol (RDP) is a proprietary protocol developed by Microsoft which provides a user with a graphical interface to connect to another computer over a network connection. The user employs RDP client software for this purpose, while t ...
*RELP, Reliable Event Logging Protocol
*RFB, Remote Framebuffer Protocol
* Rlogin, Remote Login in UNIX Systems
*RPC, Remote Procedure Call
*RTMP, Real Time Messaging Protocol
*RTP, Real-time Transport Protocol
* RTPS, Real Time Publish Subscribe
*RTSP, Real Time Streaming Protocol
*SAP, Session Announcement Protocol
*SDP, Session Description Protocol
*SIP, Session Initiation Protocol
The Session Initiation Protocol (SIP) is a signaling protocol used for initiating, maintaining, and terminating communication sessions that include voice, video and messaging applications. SIP is used in Internet telephony, in private IP telepho ...
*SLP, Service Location Protocol
The Service Location Protocol (SLP, srvloc) is a service discovery protocol that allows computers and other devices to find services in a local area network without prior configuration. SLP has been designed to scale from small, unmanaged networks ...
*SMB, Server Message Block
*SMTP, Simple Mail Transfer Protocol
*SNTP, Simple Network Time Protocol
*SSH, Secure Shell
*SSMS, Secure SMS Messaging Protocol
*TCAP, Transaction Capabilities Application Part
*TDS, Tabular Data Stream
* Tor (anonymity network)
*Tox
Tox or TOX may refer to:
Science and technology
* TOX, a protein encoded by the TOX gene
* Tox screen, medical diagnostic screening for toxic substances
Computing
* Tox (protocol), peer-to-peer instant messaging software
* tox (Python testing ...
*TSP, Time Stamp Protocol
*VTP, Virtual Terminal Protocol
* Whois (and RWhois), Remote Directory Access Protocol
* WebDAV
* WebRTC
* WebSocket
*X.400
X.400 is a suite of ITU-T Recommendations that defines the ITU-T Message Handling System (MHS).
At one time, the designers of X.400 were expecting it to be the predominant form of email, but this role has been taken by the SMTP-based Internet e-m ...
, Message Handling Service Protocol
*X.500
X.500 is a series of computer networking standards covering electronic directory services. The X.500 series was developed by the ITU-T, Telecommunication Standardization Sector of the International Telecommunication Union (ITU-T). ITU-T was former ...
, Directory Access Protocol (DAP)
*XMPP, Extensible Messaging and Presence Protocol
*Z39.50
Z39.50 is an international standard client–server, application layer communications protocol for searching and retrieving information from a database over a TCP/IP computer network, developed and maintained by the Library of Congress. It is c ...
*DNS
The Domain Name System (DNS) is a hierarchical and distributed naming system for computers, services, and other resources in the Internet or other Internet Protocol (IP) networks. It associates various information with domain names assigned to ...
, Domain Name Services
References
External links
*
*{{Wikiversity-inline, Application layer
OSI model